Method of transferring liquid

ABSTRACT

An electrostatic printer has a nozzle from which the ink is issued with an accelerating electrode and an intermediate electrode placed between the nozzle and the platen or target. A high voltage potential difference is established between the nozzle and the target with an intermediate potential being applied to the accelerating and intermediate electrodes. A sufficient potential difference exists between the nozzle and the accelerating electrode to draw the ink from the nozzle into a fine stream, and a sinusoidally varying field is superimposed on the field between the nozzle and the accelerating electrode to establish a high frequency vibration in the electrostatically charged ink stream. Droplet formation then takes place in synchronism with the sinusoidally varying field in a region of a weak field between the accelerating and intermediate electrodes which are at the same or only slightly different potentials, with the size and spacing of the droplets being controlled by the frequency of the sinusoidally varying field. As a result, droplets of substantially uniform size, substantially uniformly spaced apart, are formed.

United States Patent Inventor James M. Berry 3,281,860 10/1966 Adams et al. 346/75 [21] A l N 5mg", -J- FOREIGN PATENTS p o. Filed Dec. 1967 1,042,307 9/1966 Great Britain 346/75 [45] Patented May 18, 1971 Primary Examiner-Joseph W. Hartary [73] Assignee Teletype Corporation Attorneys-J. L. Landis and R. P. Miller Skokie, Ill.

[54] METHOD OF TRANSFERRING LIQUID An electrostatic printer has a nozzle from which 9 Claims, 2 Drawing Figs the nk 15 issued with an accelerating electrode and an intermediate electrode placed between the nozzle and the platen or U.S. 1, target A oltage potential difference established 346/75, 239/3 between the nozzle and the target with an intermediate poten- III. to the a celerating and intermediate elec- Fleld of Search l5, trodes A ufi'icient potential difi'erence exists between the 4; 346/ 1 q l li 3 l q nozzle and the accelerating electrode to draw the ink from the 1 18/ lnqull'ed); 1 17/(lnqu1TFd); 101/ (lnqulred); nozzle into a fine stream, and a sinusoidally varying field is su- 2044011991169); 346/75; 317/3 perimposed on the field between the nozzle and the acceleratin electrode to establish a high fre uenc vibration in the [56) References cued el ctrostatically charged ink stream. l)ropl et formation then UNITED STATES PATENTS takes place in synchronism with the sinusoidally varying field 3,278,940 10/ 1966 Ascoli 346/75 in a region of a weak field between the accelerating and inter- 2,512,743 6/1950 Hansel] 239/102 mediate electrodes which are at the same or only slightly dif- 2,600,129 1952 c a ds 346/75 ferent potentials, with the size and spacing of the droplets 3,060,429 10/ 1962 Winston 346/75 being controlled by the frequency of the sinusoidally varying 3,293,030 1967 Lewis et 31-" /75 field. As a result, droplets of substantially uniform size, sub- 3,281,859 10/1966 Stone 346/75 stantially uniformly spaced apart, are formed.

4 l.\\\\\\\\ \l O Patented May 18, 1971 I //T W- o INVENTOR ES M. BERRY ATTORNEY METHOD OF TRANSFERRING LIQUID BACKGROUND of the INVENTION In the field of high speed printers, the limitations of mechanical devices substantially have been overcome through the use of electrostatic printers such as the type disclosed in the patent to C..R. Winston, US. Pat. No. 3,060,429 issued Oct. 23, 1962. The printer disclosed in that patent uses electrostatic attraction between charged ink issuing from a nozzle and a platen placed behind a recording medium to attract the ink issuing from the nozzle to the recording medium. This printer provides suitable operation at high speeds of operation, the droplets formed from the stream of ink issued from the nozzle are not of uniform size and spacing so that control of individual droplets by means of deflection electrodes is very difficult. This is not a disadvantage for many applications, but in some applications it is desirable to effect precise control of each droplet formed. In order to accomplish such control, it is necessary that the droplets be of uniform size and spaced uniform distances apart.

It has been discovered that high frequency vibration of the ink stream issuing .from the nozzle causes droplets to be formed from the ink stream with substantially uniform size and spacing at a frequency which is synchronously related to the frequency of vibration of the stream. In the past, the stream has been vibrated electrically by subjecting it to a sinusoidally varying field or the noule has been vibrated electromechanically either by the use of a piezoelectric crystal or a magnetostrictive device. A problem in using electromechanical transducers is that the bond between the transducer and the nozzle may be broken by the high frequency vibration or the bond between the nozzle and the reservoir of ink may be disturbed, and the use of such transducers results in a relatively expensive structure. Irrespective of the manner in which the stream is vibrated if the charged stream is subjected to an excessive accelerating potential at the time of droplet fonnation, variations in the size or spacing of the droplets may occur.

SUMMARY of the INVENTION In accordance with this invention fluid is accelerated from a nozzle to a target by means of electrostatic attraction. The fluid is electrostatically charged and may be withdrawn from the nozzle in a manner similar to that described in the abovementioned Winston patent or it may be forced from the nozzle under pressure. A pair of electrodes are placed between the nonle and the target, and substantially the same DC potential is applied to both of these electrodes which are spaced a short distance apart. After the ink stream passes through the accelerating electrode, it breaks up into droplets in the region between the two electrodes; and since the two electrodes are at substantially the same potential, no electrostatic field or only a weak electrostatic field appears therebetween. As a result, the stream assumes a cylindrical configuration so that the breakup of the stream into droplets results in uniformly sized and uniformly spaced droplets. Once the droplets pass through the second (intermediate) electrode, they are subjected to additional electrostatic attraction, but this has no affeet on the already established droplet size or spacing, and accurate control of the individual droplet deflection then is possible.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatical view illustrating a preferred embodiment of the invention; and

FIG. 2 is an enlarged, partially cutaway, side view of the embodiment shown in FIG. 1 illustrating the manner in which the droplet formation takes place.

DETAILED DESCRIPTION Referring now to the drawings in which the same reference numerals are used in both FIGS. to designate the same elements, there is shown a fluid transferring device in accordance with the preferred embodiment of the invention. The embodiment shown in FIGS. 1 and 2 illustrates the use of the invention in an electrostatic printer of the general type disclosed in the Winston patent wherein the conductive fluid (ink) is supplied at a constant flow rate from a reservoir (not shown) to a nozzle 10 which terminates in a capillary tube 11. The nozzle 10 and the tube 11 preferably are made of one piece of electrically conductive material, and ink issuing from the tube 11 is accelerated toward a target or platen 12 by electrostatic attraction created by applying a high potential difference between the noule l0 and the platen 12.

In order to accelerate and control the flow of ink from the nozzle 11 to the platen 12, a pair of electrodes, an accelerating electrode 13 and an intermediate electrode 14, are provided. The accelerating electrode 13 is comparable to the single valving electrode used in the aforementioned Winston patent and is maintained at a positive DC potential relative to the potential on the nozzle 10 by means of a DC power supply such as the battery 15. This DC potential is of sufficient magnitude to create a strong accelerating field between the nozzle and the accelerating electrode 13, so that ink issuing from the nozzle is drawn into a fine, rapidly moving stream whenever this potential difference between the nozzle 10 and the electrode 13 exists.

The use of a strong accelerating field permits the utilization of a tube 11 having a relatively large inside diameter since the inside diameter of the tube does not alone determine the diameter of the stream of ink which is formed into droplets. As the large diameter, relatively slow-moving stream of ink issues from the end of the tube 11, it is subjected to a strong field which causes it to accelerate, and, consequently, to be drawn out into a tapered, rapidly moving stream. By the time the ink stream reaches the hole in the accelerating electrode 13, it is of considerably smaller diameter than the inside diameter of the tube 11. As a result, clogging of the tube 11 is much less a the electrode 13. Thus, the electrode 14 is maintained at substantially the same DC potential as the electrode 13, being illustrated in FIGS. 1 and 2 by the showing of a battery 16 in dotted lines between the electrodes 13 and 14. As a consequence, only a relatively weak DC field or no DC field exists between the electrodes 13 and 14; so that the stream of charged ink particles passing through the hole in the electrode 13 is not subjected to an electrostatic force of any consequence in the region between the electrodes 13 and 14. It is in this region that the droplet formation takes place from the stream of ink issuing from the tube ll.

After the ink droplets pass through the hole in the intermediate electrode 14, they then are deflected in the vertical and horizontal directions under control of deflection potentials applied to a pair of vertical deflection plates 17 and a pair of horizontal deflection plates 18. These sets of deflection plates both have applied to them components of DC potentials which are more positive than the potential on the electrode 14, so that ink droplets, after passing through the hole in the electrode 14, are further accelerated. The deflection signals are superimposed on this component of DC potential applied to the deflection electrodes in order to direct the ink particles to selected areas on the platen 12. The platen 12 in turn is maintained at a potential which is more positive than the DC potential applied to the horizontal deflection electrodes 18 and which is obtained from a suitable source such as a battery 19.

In order to precisely control the size of the droplets formed and the spacing between the droplets, it is desirable to introduce a pulsation or oscillation into the ink stream issuing from the nozzle 11. This may be accomplished by mechanically vibrating the nozzle or by superimposing a periodically varying signal, such as an AC sinusoidal signal, on the field between the nozzle and the first valving electrode 13. As shown in the drawings, an AC generator 20 is connected in series with the battery between the nozzle 10 and the accelerating electrode 13 to cause the field betweenthem to fluctuate sinusoidally, resulting in the formation of periodic disturbances in the ink stream being withdrawn from the nozzle. The voltage of the AC generator is chosen to be such that the field between the nozzle 10 and the electrode 13 fluctuates sinusoidally without ever swinging negative; that is, the peak-to-peak value of the signal generated by the generator 20 does not exceed twice the potential of the battery 15. The frequencies used have ranged from L4 kHz. to kHz. but this range is not to be construed as limiting.

The periodic disturbances created in the stream of ink flowing from the nozzle 10 cause the formation of droplets in synchronization with the disturbances, and the stream breaks up into droplets in the region of weak field between the electrodes 13 and 14. This region of weak field in the area of droplet formation appears to be necessary due to the fact that when the stream of ink is subjected to an accelerating field, it is tapered in form rather than cylindrical. When a segment of a tapered stream of ink breaks off from the stream, it has been observed that the entire segment does not always form into a single droplet, but that a large droplet and one or more smaller droplets may form. from the segment or that two or more droplets of equal size may form. At other times a single droplet forms as desired. Because the number and size of droplets cannot accurately be controlled when the stream is being accelerated, the intermediate electrode 14, held at substantially the same potential as the electrode 13, causes a weak field region to exist in which the stream assumes a cylindrical configuration. Thus, the stream no longer is subjected to accelerating forces in this region, and the disturbances introduced into the stream cause' it to breakup into uniform cylindrical segments. Each of these segments then forms into a single droplet, so that all of the droplets formed are of uniform size. As a result, the droplets are completely formed prior to passing through the hole in the electrode 14, whereupon they are further accelerated by the potential appearing on the vertical deflection electrodes 17, as described previously.

The actual voltages which must be applied to the nozzle and the various electrodes depend on many factors, in particular on the ink flow rate, the droplet frequency, the dimensions and spacing of the various electrodes, and the physical and electrical characteristics of the ink. The same relative conditions must exist, however, in all cases, namely, sufficient potential must exist between the noule l0 and the accelerating electrode 13 to fonn the ink issuing from the nozzle into a jet and a region of weak field must exist between the electrodes 13 and 14, whereupon further acceleration of the completely fonned droplets then may take place between the electrode 14 and the platen or target 12 which is at a substantially higher DC potential than the electrode 14.

Although the illustration of the preferred embodiment indicates that the nozzle is at a relatively negative DC potential compared to the potentials applied to the other electrodes, it should be apparent that the reverse could also be true, with the nozzle 10 being at a positive potential relative to the other electrodes. All that is necessary is that the ink be charged to a potential which is opposite to the potential applied to the target or platen,'and that the relative voltages be of sufficient magnitude to withdraw and accelerate the ink to the platen.

In the foregoing description of the preferred embodiment of the invention, anAC potential is applied to the nozzle 10 in order to cause a cyclically varying field to occur between the nozzle 10 and the first valving electrode 13. A similar result can be attained by using a piezoelectric crystal or the like to vibrate the nozzle 10 and the capillary tube 11 at the desired frequency. If this type of configuration is employed, the nozzle synchronous ink droplet formation otherwise is identical to that described above in conjunction with FIGS. 1 and 2.

Although the invention has been described as being used to transfer ink in an electrostatic printer, it also may be used in a fluid transferring apparatus and method for precisely measuring and transferring predetermined amounts of fluid from a reservoir to a target receptacle. Various changes and modifications to the apparatus and its method of operation, as described in conjunction with the preferred embodiment, will occur to those skilled in the art, and the invention is not to be considered limited to the embodiment chosen for purpose of disclosure butv encompasses all modifications and changes lying within the true scope of the invention.

l claim: 1. A method of forming a series of droplets of liquid of substantially uniform size and spacing including the steps of:

forming a stream of liquid substantially on an axis; applying substantially the same electric potential to a pair of axially-spaced electrodes; directing the stream of liquidinto the region between the electrodes to cause the stream of liquid to assume substantially a cylindrical configuration; and controlling at least one characteristic of the stream of liquid to cause the stream of liquid to break into droplets in the region between the electrodes. 2. A method according to claim 1 including the additional step of creating periodic disturbances in the stream of liquid further to induce the droplets formed to be of uniform size.

3. A method according to claim 1 including the additional step of accelerating the stream of liquid before it enters the region between the electrodes.

4. A method of controlled droplet formation of a liquid stream including the steps of:

forming a solid stream of liquid flowing in a gas by applying an electrostatic accelerating force to said stream of liquid in a first region; and v applying substantially zero accelerating force to said stream in a second region to cause the stream to assume a substantially cylindrical configuration in said second region; and

controlling at least one characteristic of the stream of liquid to cause the stream of liquid to break into droplets substantially in said second region.

5. A method of fonning droplets of uniform size from a liquid including the steps of:

forming a solid stream of liquid flowing in a gas;

creating periodic disturbances in the stream of liquid to cause segments of the stream to break off and form droplets in synchronism with the disturbances;

applying an accelerating force to the stream of liquid; and

reducing to substantially zero the accelerating force acting on the stream in the region where the droplet formation takes place to cause the stream of liquid to assume substantially a cylindrical configuration in the region where droplet formation takes place.

6. A method according to claim 5 including the additional step of imparting an electrostatic charge to the stream of liquid and wherein the accelerating force is an electrostatic field.

7. A method of forming droplets from a stream of liquid including the steps of:

imparting an electrostatic charge to a stream of liquid;

subjecting the charged stream of liquid to an electrostatic field to accelerate the stream of liquid;

imparting periodic disturbances to the stream of liquid to cause it to break up into droplets in synchronism with the disturbances; and

establishing an electrostatic field of substantially zero electrostatic potential in the region where the stream breaks up into droplets to cause the stream of liquid to assume substantially a cylindrical configuration in said region.

8. A method according to claim 7 wherein the field in the 10 is held at a predetermined DC potential, but the region where the stream breaks up into droplets is established substantially a cylindrical configuration in the second region, thereby facilitating droplet formation in said second region;

controlling at least one characteristic of the stream of liquid to cause the stream to break into droplets substantially in the second region; and

positioning the record medium in the path of said stream of ink. 

1. A method of forming a series of droplets of liquid of substantially uniform size and spacing including the steps of: forming a stream of liquid substantially on an axis; applying substantially the same electric potential to a pair of axially-spaced electrodes; directing the stream of liquid into the region between the electrodes to cause the stream of liquid to assume substantially a cylindrical configuration; and controlling at least one characteristic of the stream of liquid to cause the stream of liquid to break into droplets in the region between the electrodes.
 2. A method according to claim 1 including the additional step of creating periodic disturbancEs in the stream of liquid further to induce the droplets formed to be of uniform size.
 3. A method according to claim 1 including the additional step of accelerating the stream of liquid before it enters the region between the electrodes.
 4. A method of controlled droplet formation of a liquid stream including the steps of: forming a solid stream of liquid flowing in a gas by applying an electrostatic accelerating force to said stream of liquid in a first region; and applying substantially zero accelerating force to said stream in a second region to cause the stream to assume a substantially cylindrical configuration in said second region; and controlling at least one characteristic of the stream of liquid to cause the stream of liquid to break into droplets substantially in said second region.
 5. A method of forming droplets of uniform size from a liquid including the steps of: forming a solid stream of liquid flowing in a gas; creating periodic disturbances in the stream of liquid to cause segments of the stream to break off and form droplets in synchronism with the disturbances; applying an accelerating force to the stream of liquid; and reducing to substantially zero the accelerating force acting on the stream in the region where the droplet formation takes place to cause the stream of liquid to assume substantially a cylindrical configuration in the region where droplet formation takes place.
 6. A method according to claim 5 including the additional step of imparting an electrostatic charge to the stream of liquid and wherein the accelerating force is an electrostatic field.
 7. A method of forming droplets from a stream of liquid including the steps of: imparting an electrostatic charge to a stream of liquid; subjecting the charged stream of liquid to an electrostatic field to accelerate the stream of liquid; imparting periodic disturbances to the stream of liquid to cause it to break up into droplets in synchronism with the disturbances; and establishing an electrostatic field of substantially zero electrostatic potential in the region where the stream breaks up into droplets to cause the stream of liquid to assume substantially a cylindrical configuration in said region.
 8. A method according to claim 7 wherein the field in the region where the stream breaks up into droplets is established between a pair of spaced electrodes by applying substantially the same potential to both electrodes.
 9. A method of controlled droplet formation of a stream of liquid ink flowing onto a record medium including the steps of: forming a solid stream of liquid flowing in a gas by applying an electrostatic accelerating force to said stream of liquid ink in a first region; applying substantially zero accelerating force to said stream in a second region to cause the stream of liquid to assume substantially a cylindrical configuration in the second region, thereby facilitating droplet formation in said second region; controlling at least one characteristic of the stream of liquid to cause the stream to break into droplets substantially in the second region; and positioning the record medium in the path of said stream of ink. 